The meanings of the words a,an and the are less specific than the meanings of the other determiners. A, an and the are sometimes referred to as articles. They are the determiners most frequently used with singular countable nouns.
The is definite article in English, it used for denoting person( s ) or thing( s ). It is often used as the very first part of a noun phrase.
Sometimes the presence or absence or the in a sentence is irrelevant; the person quoted could have employed either usage: “She’ll have the strawberry cheesecake” identifies the particular dessert a diner wishes to be served, one either visible to the speaker or listed on a menu — a literal or implied second reference. “She’ll have strawberry cheesecake” means the same thing — with the subtle difference that the speaker is not directly alluding to the dessert selection visible in the form of a slice or a reference in text.
The man who walking over there is my dad.
The King has two daughters.
Singular countable nouns must usually be preceded by determiners even when the nouns are also preceded by various descriptive words. As well as being used before words beginning with consonants, a and an are also used before words which begin with vowels, but which are pronounced with an initial consonant sound. For instance, a and an are used before words beginning with eu and words beginning with a long u, since these words are pronounced with an initial y sound. A and an are also used before the word one, since one is pronounced with an initial w sound.
I need a cup of coffee right now.
She bought an eraser at the bookstore last night